There are known three typical conventional methods for forming optical wiring. A first method comprises the steps of coating a glass film or a polymer film having high transmittance for light on a substrate, and forming the optical wiring on the substrate in a similar manner to that used for forming a circuit pattern in the LSI production process. More specifically, according to this first method, the optical wiring is formed by coating a photoresist on the surface of the glass film or the polymer film, exposing the photoresist to light through a mask having an optical wiring pattern, and removing unnecessary portions by etching. When a core portion and a clad portion are formed, the above-mentioned steps are repeated at least twice.
The first method is advantageous in, for example, capabilities of drawing a complicated pattern and forming an optical device as well. On the other hand, the first method has such shortcomings that a large-scale semiconductor facility is required, large-sized wiring cannot be produced, and wiring for connection between substrates cannot be formed.
A second method uses optical fibers to form optical wiring. This second method is simple, but it has such shortcomings that the wiring is unstable and requires a larger space, because the wiring is formed just by arranging the optical fibers in the form of bundles and fixing them by wires. Also, when the number of bundled optical fibers increases, a difficulty arises in managing how the optical fibers are connected.
According to a third method, an optical fiber is held and fixed between polymer sheets (Patent Document 1). This third method is advantageous in that, because the wiring is given in the patterned form, the fiber management is simple even when the number of optical fibers increases, and that a large-scale facility is not required. However, because of the structure holding the optical fiber between polymer sheets, the third method cannot form the optical wiring on a plate connecting substrates.
Patent Document 1: Japanese Patent Laid-Open No. 11-119033